As one of the conventional backlights of display devices such as liquid crystal display devices, the following device is known. The device comprises a light source which emits polarized light such as laser light, and a lightguide plate which irradiates a display panel with the laser light emitted from the light source.
To obtain, for example, white light with the backlight using polarized light, there is a need to prepare light sources which emit red light, green light and blue light and mix the light emitted from the light sources. The backlight which obtains light in a specific color by mixing polarized light in different colors has various problems.
For example, when polarized light are mixed such that the optical axes are aligned before the light reach the lightguide plate, a space is required to provide an optical system for aligning the light axes. Thus, it is difficult to reduce the size of backlight.
When the polarized light from each light source directly enters the lightguide plate, and the light are mixed in the lightguide plate, the lightguide plate is difficult to equalize surface emission because, for example, the spread angle of polarized light is less.